Availability and Downtime in SQL Server Context

What is Availability ?

Availability is generally driven by the application and defined in the SLA (Service Level Agreement). For Eg. An order processing system the client requirement may be an Order should be completed in 1 sec. And also there will be a mention of acceptable downtime also. It may be 5 min/1 hr/1 day as per the requirement.


Downtime

Downtime is the time when the SLA is not met. There are two type of downtime :-


(a) Planned Downtime : It’s the time when you upgrade your system or apply patches or any kind of periodic maintenance of the system. It will be mentioned in the SLA.

(b) Unplanned downtime : May be because of human error or system corruption or natural calamity etc etc.